1. Field of the invention
The invention relates to a jack and, in particular, to a vehicle jack which can be used for lifting and/or lowering a vehicle and which can also be carried along in said vehicle, e.g. a motor car.
2. Description of the prior art
A vehicle jack disclosed in the French patent 552 918 comprises a support supporting a first and a second bevel gearwheel and a transferring means which is operatively connecting the second gearwheel with a load carrier for engaging a load. A base plate of the support and the second gearwheel comprise annular grooves which guide together a set of balls. The base plate, balls and second gearwheel form together a ball bearing. The quoted French patent doesn't disclose the manufacturing of the jack. However, the shapes and great material thicknesses of the base plate, second gearwheel and other parts indicate that the base plate, the gearwheels and also various parts of the transferring means are manufactured substantially by chip removal operations--such as turning and milling--or possibly by casting and by subsequent chip removal operations. Manufacturing the base plate, the gearwheels and other parts of the jack at least partly by chip removal operations needs a lot of time, entails considerable costs and gives rise to waste material which gets "lost" and must be disposed of. A jack of the kind shown in the French patent has moreover a relatively great weight. This is particularly disadvantageous for vehicle jacks intended to be carried along in a motor car or other vehicle.
The U.S. Pat. No. 3,862,577 discloses a screw jack which possesses a support, a first gearwheel, a second gearwheel and a transferring means connecting the second gearwheel operatively with a load carrier. The second gearwheel, viz. the crown gear, is supported by a sliding bearing means which has the drawback that it gives a relatively high friction. The first gearwheel, viz. the pinion, is manufactured by cutting a cylindrical blank which is then submitted to five plastic shaping operations by means of different dies. Although the teeth of the first gearwheel are formed by plastic shaping, the manufacturing of this gearwheel is expensive because it requires a great number of shaping operations and of different dies. The manufacturing of the second gearwheel, i.e. the crown gear, is not disclosed in the U.S. patent. It appears as probable that the second gearwheel is produced in a conventional manner, in which the second gearwheel and particularly the teeth thereof are formed at least partly by costly chip removal operations.
The German patent application 1 287 549 discloses the production of spur-toothed wheels and of bevel gears by rolling, i.e. flow-turning, blanks which consist of cylindrical rings or annular disks. A blank to be shaped is inserted into a die which has a toothed surface and is then rotated together with the blank. During rotation of the die, a roller is displaced in such a manner that it presses the blank sucessively into the die. Such a shaping operation takes still quite a long time and requires a very precise positioning and displacement of the roller so that gearwheels manufactured in this manner are still expensive. The German patent application contains by the way no information how the gearwheels are to be supported and what they may be used for.